1. Field of the Invention
The present invention relates generally to a display drive device and a method for driving the same, as well as a display device and a method for driving the same, and more particularly to a display drive device for driving a plurality of display pixels having light emitting elements that emit light when supplied with a current, a display device including the display drive device and methods for driving the display drive device and the display device.
2. Description of the Related Art
In recent years, in an effort to replace a liquid crystal display device, research and development efforts have been actively made to develop a light emitting element type display device (light emitting device type display) including a display panel on which organic electroluminescence elements (organic EL elements), or inorganic electroluminescence elements (inorganic EL elements), or current-driven light emitting elements such as a light emitting diode (LED), are arranged in a matrix (or matrix shape).
In particular, a light emitting element type display using an active matrix driving system has an extremely advantageous feature in that, in comparison with known liquid crystal display devices, the display response speed is high and the viewing angle dependency is small, making it possible to achieve high image quality, in particular, high luminance/high contrast and high resolution. Further, it is not necessary to provide a backlight or a light guiding plate (which are necessary for a liquid crystal display device), thus making it possible to obtain a display having a small thickness and light weight. Therefore, application of this type of display to a variety of electronic devices is expected in the future.
This type of light emitting element display is configured such that a pixel drive circuit is provided for each display pixel. The circuit includes a current control thin film transistor (TFT) in which a voltage signal corresponding to image data is applied to a gate to supply a current to an organic EL element, and a switching thin film transistor that carries out a switching operation for supplying the voltage signal that corresponds to the image data to the gate of the current control thin film transistor. Gradation control of display pixels in such a display includes supplying each of the display pixels with a gradation voltage having a voltage value that corresponds to display data, holding in the pixel drive circuit a voltage component that corresponds to a current flowing in response to the supplied gradation voltage, and supplying a driving current to a light emitting element, based on the held voltage component, thereby controlling light emitting luminance.
However, in the current control thin film transistor, a threshold value may vary with time (as time elapses). In this case, in a system of supplying the gradation voltage to display pixels to effect gradation control as described above, if there is a threshold value fluctuation over time, then even if the same gradation voltage is supplied, a value of a driving current flowing into a light emitting element fluctuates.